Lecture 3 - Bacterial Structure

prokaryotic cells

simple cells (no nucleus or organelles), always in singles, represented in domain bacteria and domain archaea

structures found in all bacteria

cell membrane, bacterial chromosome/nucleoid, ribosomes, cytoplasm

structures found in some bacteria

S layer, fimbriae, outer membrane, cell wall, actin cytoskeleton, pilus, capsule, inclusion/granule, bacterial microcompartments, plasmid, endospores, intracellular membranes

external parts of bacterial cells

flagella, pili, fimbriae, S layer, glycocalyx (capsule & slime layer)

cell border of bacterial cell

cell wall, cell membrane

internal structures of bacterial cells

ribosomes, inclusions, nucleoid/chromosome, endospore, plasmid

flagella

whip-like tail for motility/self-propulsion, can guide bacteria in a specific direction, light/chemical stimuli set in motion

run

flagella rotate counterclockwise and cell moves in an smooth linear direction towards stimulus

tumble

flagella rotate clockwise and cell stops and changes course

flagella arrangements

monotrichous, lophotrichous, amphitrichous, peritrichous

monotrichous

single flagellum at one end

lophotrichous

small bunches emerging from same site

amphitrichous

flagella at both ends of cell

peritrichous

flagella dispersed over surface of cell

axial filaments

bundles of flagella wrapped around length of bacteria for motility, spiral the length of the cell, only found in spirochaetes, contract for a flexing motion

fimbriae

small, bristle-like fibers on surface, help w/adhering to surface, help pathogens like E. coli (virulence factor)

pili

tube-like structures that function to join bacteria together for DNA transfer called conjugation or can help w/adhering to surfaces

S layer

tons of a single protein linked to form a tight covering around cell; very outer layer; only produced when bacterium finds itself in a hostile environment

glycocalyx

under S layer; polysaccharide; helps w/adherence and formation of biofilms; differ among bacteria; can be slime layer or capsule

slime layer

loose glycocalyx used for protection from dehydration and loss of nutrients, helps w/adhesion

capsule

bound more tightly; thick and sticky; formed by many pathogenic bacteria (helps protect bacteria against phagocytes); if the bacteria mutate to nonencapsulated, usually lose their pathogenicity

cell wall

determines shape of bacterium, provides structural support, helps prevent rupture from osmotic pressure

peptidoglycan

unique to bacterial cell walls, provides strength and stability

Gram-positive cell wall

mostly thick layer of peptidoglycan, plus teichoic acid and lipoteichoic acid

Gram-negative cell wall

more complex, outer membrane + thin layer of peptidoglycan

outer membrane

lipopolysaccharides and lipoproteins — lipid portion of LPS may become toxic when released during infection

Gram stain procedure

differentiates between gram-positive and gram-negative cell wall

primary stain

crystal violet

mordant

iodine

decolorizer

alcohol

secondary stain

safranin

Gram-positive result

crystal violet & iodine form giant crystals that get trapped in thick peptidoglycan, purple cells

Gram-negative result

crystal violet & iodine form giant crystals > alcohol dissolves outer membrane and leaves holes in thin peptidoglycan > purple color washes out > safranin added to colorless cells > pink

atypical cell walls

• several bacterial groups don’t have a gram-positive/negative cell wall

  • mycobacterium have unique lipids and best viewed w/acid fast stain

• some lack a cell wall (mycoplasmas)

gram negatives

-outer membrane in gram negative makes them harder to inhibit/kill b/c later makes them more impervious to chemicals

-LPS stimulates fever and shock in gram negative infections like meningitis and typhoid fever

gram positive

proteins attached to cell wall of certain gram-positive species like Streptococcus pyogenes and Corynebacterium diphtheriae have toxic properties

acid fast

lipids in certain species of Mycobacterium are harmful to humans

cell membrane

continuous sheet around cytoplasm, lipid bilayer w/embedded proteins

functions of cell membrane

-barrier; regulates transport through selective permeability

-site of energy reactions, nutrient processing and synthesis

cytoplasm

mostly water w/nutrients mixed in, contains larger bodies like chromosome, ribosomes, and granules/inclusionswhich provide support and facilitate metabolic processes in bacterial cells.

nucleoid

composed of DNA molecules, DNA found in the form of a single circular chromosome

plasmids

additional genetic elements made up of small circular pieces of DNA, exist independently in cytoplasm

ribosome function

site of protein synthesis

ribosome structure

made of RNA and protein, consists of two subunits (large, small), dispersed in cytoplasm or attached to cell membrane

inclusions/inclusion bodies

storehouses of nutrients like glycogen and poly β-hydroxybutyrate (PHB), can also include gas vesicles that provide buoyancy and flotation in some aquatic bacteria

granules

inorganic compounds like sulfur & polyphosphate

magnetosomes

contain iron oxide and act as magnets to help w/navigation

endospores

microbial structure for surviving hostile conditions, not produced by all bacteria, produced by Bacillus, Clostridium and a few others, has a two phase life cycle; shifts between vegetative cell and endospore

sporulation

formation of spore, major stimulus for sporulation is depletion of nutrients, takes about 6-12 hours, can withstand extremes in heat, drying, freezing, radiation, and chemicals

germination

returning to vegetative state in presence of water and a specific germination agent (varies among species)

coccus (cocci)

ball shaped/spherical

bacillus

rod/cylindrical

vibrio

curved rod

spirillum

spiral-shaped, rigid

spirochete

spiral-shaped, flexible, springy

pleomorphism

variation in cell shape and size in a single species

cell arrangements

influenced by pattern of division and how cells remain attached afterward

singles

one

pairs

diplo-

chains

strepto-

tetrads

four

sarcina

cubical packet of 8, 16 or more

irregular clusters

staphylococci and micrococci

Staphylococcus

members causeboils, skin infections

Streptococcus

species cause strepthroat, cavities

Bacillus

anthrax

Clostridium

tetanus, gas gangrene, botulism

Clostrioides

C-diff disease

Neisseria

gonorrhea, meningitis

Escherichia, Edwardsiella, Cirobacter, Salmonella

typhoid fever

Shigella

dysentery

Klebsiella, Enterobacter, Serratia, Proteus, Yersinia

one species causes plague

cyanobacteria

photosynthetic; aquatic; very different structures and arrangementsgr

green & purple sulfur bacteria

photosynthetic but do not produce oxygen during the process

Rickettsias

tiny Gram-negative parasites (cannot live/divide outside of host cell), transmitted by insects like ticks or lice; cause Rocky Mountain Spotted Fever and typhus

archaeans

extremophiles and live in unusual environments